On x86, there are two levels of partitions: fdisk partitions, and within the Solaris partition, "slices". Something ending in p0 is the whole disk; p1 through p4 are each an entire fdisk partition; something ending in s0 through s15 is a Solaris slice (within the Solaris fdisk partition). By convention, s2 encompasses the entire fdisk partition that contains it. Usually, s0 is root, and s1 is swap. The others need not be used unless one wants more filesystems (splitting out /var or /export/home, for example).
Any given OS can only own one primary (fdisk) partition on a disk. Solaris cannot be installed into a logical partition (subdivision of an extended fdisk partition). It's ability to address logical partitions is AFAIK limited to pcfs, where you might see a filesystem mounted from something like /dev/dsk/c0t0d0p2:d (a colon letter or colon number suffix indicating a logical partition within p2). I don't promise that I got that last paragraph right... Hope that helps. Now, I'm going to start rambling, and get really confusing (and confused). On SPARC, disks don't normally have fdisk partitions, they have a Sun VTOC with Solaris slices 0 through 7. However, for a non-boot disk, fdisk partitions can be recognized, so that for example pcfs (FAT) filesystems on a USB drive can be read. Complicating all the above is EFI, an alternative to fdisk partitions. Both x86 and SPARC can handle it at the OS level. It doesn't need extended+logical partitions, because it allows more than four. I would suppose (but haven't checked) that on x86 the OS could boot from an EFI partition if the BIOS supported it. I'm not aware of any OpenBoot firmware for SPARC that can boot from an EFI partition. If zfs is given an entire disk, I think it will set it up as a single EFI partition (and default to enabling drive write cache, issuing cache flush commands as needed to ensure consistency). Not sure what happens when one has a boot disk (that at least on SPARC AFAIK can't be EFI) where zfs has the whole disk...whether or not it would enable the disk's write cache. It is all (IMO) a bit confusing...would be nice to see the device naming conventions fully spelled out with examples, for both x86 and Solaris. And I think there have been a lot of requests to be able to install into a logical partition for multiboot configurations (esp since I think Linux can do that). One problem with that might be that it would mean rearranging the minor devices to reflect the presence of an additional type of partitioning, which would mess with existing installations. A good solution might not be easy, and newer systems should support EFI which doesn't need logical partitions, so (I'm guessing) despite the demand, there's not much incentive to go to all that trouble. So it's flexible, but for some people trying to run more than four OSs on a system that can only recognize fdisk labels, it's not ideal... -- This message posted from opensolaris.org
